London has been battered by 50mph winds that have felled trees and caused travel chaos. Powerful gusts swept across the capital as the Met Office issued a yellow "be aware" weather alert for most of the country.

Boris Johnson was on collision course with London's transport unions today after holding talks on possible new laws to curb strikes.

The Mayor has urged ministers to consider proposals for legislation to prevent walkouts where only a small fraction of the workforce votes in favour, sources said.

Mr Johnson is understood to be concerned that the unions are a block to reform of the Underground and other transport systems.

Transport Secretary Philip Hammond is sympathetic to the idea, although government insiders said there were no firm proposals on the table.

Chancellor George Osborne has called for spending cuts of 20 per cent or more at most departments, and a government source said: "We have a railway that is 40 per cent more expensive than other countries. Everyone knows we need to find a lot of efficiency savings."

Mr Johnson backed a minimum turnout for strike ballots after the RMT union last year held stoppages after fewer than a third of members took part in a vote. The CBI later worked up proposals where a strike would only be lawful if 40 per cent of the workforce voted in favour.

Bob Crow, the general secretary of the RMT, claimed ministers were afraid that the unions would stop cuts. "They are running scared and are now looking to tighten the noose of the anti-union laws around the workers' necks to choke off resistance," he said.

He said a 40 per cent minimum support was tougher than the rules for electing MPs. "This is a declaration of war on the trade union movement and our response will be robust as we lay down plans for co-ordinated and generalised industrial and community action against the cuts," he added.

Paul Kenny, general secretary of the GMB, said: "It is a testament to the priorities of this Government, led by two public school boys, that they should consider attacking the rights of ordinary workers rather than the bankers who caused the recession."

A spokesman for the Association of Train Operating Companies called on the RMT to be constructive. "It is our shared responsibility, across the industry and with the Government, to put rail on a more stable and sustainable footing," he said.